In recent years, in the industrial production processes of chemical substances, reactions that minimize the environmental pollution is regarded as being important. Oxidation of alcohols is one of the important chemical reactions, so that the development of reaction that has a high applicability and that does not give adverse effects to the environment is desired.
Non-patent document 1 discloses oxidation of alcohols with use of hydrogen peroxide solution and a tungsten catalyst. However, in order to allow the reaction to proceed smoothly, a condition with a pH value of 3 or below is required, and it is disclosed that the reaction wherein pH value is 3.2 gives a yield of 57%, and the reaction wherein pH value is 4.4 lowers gives the yield to be 27%. Also, according to the process disclosed in the document, the reaction is carried out with no solvent or with use of toluene as a solvent. Therefore, it has been difficult to apply the reaction disclosed in the document to the oxidation of compounds that are unstable to acid or compounds that are insoluble to toluene.
Non-patent document 2 discloses oxidation of an alcohol with use of hydrogen peroxide solution and peroxotungstate; however, it uses 90% hydrogen peroxide solution, so that it is unsuitable for mass synthesis because of the danger of explosion. It does not refer to use of any amide solvent or the pH value in the reaction conditions.
Non-patent document 3 discloses oxidation of alcohols with use of hydrogen peroxide solution and sodium tungstate. However, it discloses that, when a tungsten catalyst is used, a pH value of 1.4 is preferable and, when the acidity lowers, the selectivity of reaction decreases considerably. Since a halogenated carbon solvent is used, it is not preferable also in view of the environment. It has a problem such as using 70% hydrogen peroxide solution that is highly dangerous.
Patent document 1 discloses a process of producing carboxylic acid by oxidizing an oily solution of alicyclic alcohol or an oily solution of alicyclic ketone in a non-homogeneous solution system with use of hydrogen peroxide solution and tungstic acid. However, this document also fails to refer to use of an amide solvent and the pH value in the reaction condition.
Non-patent documents 4 to 7 and 10 disclose a process of epoxidation of olefin, a process of producing adipic acid from cyclohexane, cyclohexanol, or cyclohexanone, a process of producing sulfoxide or a sulfone compound from sulfide, a process of producing methylsulfinyl compound from a methylthio compound, or the like with use of hydrogen peroxide solution and a tungsten catalyst.
Patent documents 2 to 4 disclose oxidation with use of hydrogen peroxide and tungstate under a neutral or basic condition. Patent documents 4 and 5 disclose that N,N-dimethylacetamide can be used in the oxidation with use of hydrogen peroxide solution and tungstate. However, none of these disclose oxidation of alcohols.
Ketooleanolic acid represented by the formula (II):
(wherein R1 is hydrogen or lower alkyl)(hereafter referred to as compound (II)) is a compound that can be an intermediate of a compound represented by the formula (A):
(wherein R2 is hydrogen or —R3-R4; R3 is —SO3—, —CH2COO—, —COCOO—, or —COR5COO— wherein R5 represents alkylene having a carbon number of 1 to 6 or alkenylene having a carbon number of 2 to 6; and R4 represents hydrogen or alkyl having a carbon number of 1 to 6) (hereafter referred to as compound A), or a pharmaceutically acceptable salt thereof.
The compound A is known to be useful as a drug for treating various circulatory organ diseases (for example, high blood pressure, ischemic diseases, cerebral circulation disorders, renal disorders, circulation failure of various organs, asthma, stroke, brain infarction, brain edema, and others) (See patent documents 6 and 7), and the synthesis process of compound A is disclosed in patent documents 8, 9, non-patent documents 8 and 9, and others.
Patent document 8 and non-patent document 9 disclose a process of oxidizing oleanolic acid in chloroform-acetone or dichloromethane-acetone solvent with use of a Jones reagent; however, it necessitates use of an environmentally harmful reagent such as chromic acid, chloroform, dichloromethane or the like, so that it has not necessarily been a satisfactory process as an industrial production process.    Patent document 1 International Patent Publication WO2004/011412 Pamphlet    Patent document 2 Japanese Patent Application Laid-Open (JP-A) No. 60-132952 Gazette    Patent document 3 Japanese Patent Application Laid-Open (JP-A) No. 63-190898 Gazette    Patent document 4 Japanese Patent Application Laid-Open (JP-A) No. 2002-241631 Gazette    Patent document 5 Japanese Patent Application Laid-Open (JP-A) No. 09-118687 Gazette    Patent document 6 International Patent Publication WO92/12991 Pamphlet    Patent document 7 Japanese Patent Application Laid-Open (JP-A) No. 07-53484 Gazette    Patent document 8 Japanese Patent Application Laid-Open (JP-A) No. 07-316188 Gazette    Patent document 9 International Patent Publication WO2003/80643 Pamphlet    Non-patent document 1 Bulletin of Chemical Society of Japan, 1999, Vol. 72, p. 2287-2306    Non-patent document 2 Journal of Organic Chemistry, 1979, Vol. 44, p. 921-924    Non-patent document 3 Journal of Organic Chemistry, 1986, Vol. 51, p. 2661-2663    Non-patent document 4 Bulletin of Chemical Society of Japan, 1997, Vol. 70, p. 905-915    Non-patent document 5 Science, 1998, Vol. 281, p. 1646-1647    Non-patent document 6 Tetrahedron, 2001, Vol. 57, p.    Non-patent document 7 Journal of Organic Chemistry, 1983, Vol. 48, p. 3831-3833    Non-patent document 8 Organic Process Research And Development, 1999, Vol. 3, p. 347-351    Non-patent document 9 Journal of Organic Chemistry, 1997, Vol. 62, p. 960-966    Non-patent document 10 Green Chemistry, 2003, Vol. 5, p. 373